1. Technical Field
The present invention relates to an autofocus system, and more particularly, to a system that automatically tracks an AF frame using pattern matching.
2. Related Art
In the autofocus (AF) systems according to the related art that automatically focus cameras, it is necessary to control the camera to be focused (control the focus position of the camera). In this case, in a general camera, a focus position is fixed to the center of an photographing range. For example, the camera is focused on a person who is disposed at the center of the photographing range. Therefore, as an autofocus (AF) type, a contrast type has been used which detects the contrast of a subject image from the image signals acquired by an image pickup device and controls the focus of an photographing lens such that the contrast becomes the maximum, thereby performing autofocus in a best focus state.
The range of a subject to be subjected to AF in the photographing range of the camera or the range of a subject to be subjected to AF on the screen of the photographing image taken by the camera when the photographing image is reproduced is referred to as an AF area, and a frame indicating the outline of the AF area is referred to as an AF frame.
However, for example, when a moving subject is taken, the fixed focus position causes problems. For example, when a television camera is used to take a subject with a large amount of movement as in sports, in order to detect a target subject in focus from the photographing image and track the detected target subject, the following technique has been proposed which stores the image of a subject to be focused (focus target) as a reference pattern, detects an image that is most closely matched with the reference pattern image from the photographing image of a newly loaded frame using pattern matching, and detects the position of a target subject (for example, see Patent Document 1 (JP-A-2006-258944 corresponding to US-A-2006/0210260)).
However, as in the related art, when pattern matching is used in an algorithm for automatically tracking the AF frame, for example, the following problems arise. When there is a plurality of similar patterns in the screen as in sports in which there is a plurality of players with in the same uniform, a tracking error is likely to occur.